Process of vulcanizing rubber and product thereby obtained



N Drawing.

Patented Oct. 7, 1930 T TE 1 E l WINFIELD scorn, ornrrn wnsr VIRGINJfA, AssIGNoRTo rnnnunnnn jsnnvicn LABORATQRIES 00 on AKRON, onro, A CORPORATION or onto The present invention relates to of manufacturing vulcanized rubber} of highv quality, andithas, for itsprimary object,

the provision of accelerators of characteris tic curing powers,which maybe employed in the production of such rubber.

- Mercapto-benzoethiazole having the 'forandvvh'ich is bne'of the-many reaction prodvalue, but I have now'found thatits usefulness can be greatly increased by reacting it with certain other compounds which are p hereinafter fully describedan-d using thermaterials so obtained as accelerators.

Mercapto compounds are somevvhat acidic.

in nature, duetothe presence of the SH group contained therein, and Will therefore formsalts with various metals, and will also react Wit-hthe more stable andless volatile of organicbases to form compoundswhich maybe termed salts, and Which'themselves possess particularly high value as accelerators ofthe rubber vulcanization'process as is hereinafter set forth. Certain of the metallic saltsof mercapto compounds-havegalready been described as vulcanization accelerators, but my invention is concernedvvit-hthe use of the more powerful accelerating materials hereinafter descr bed in detall; In fact, I

may conclude frolnthe experiments herein} after set forth in lnorej detail, that a inc reap-v tan or a derivative of amercaptan, to display 0 its accelerating properties to the greatest dc gree, preferably should have within the molec'ule, son'1e group or groupingvvliich' illtend more or less completely to. counteract the acidic nature of the 'SH group. Extensive experimentation, carried out-on thisproblem,

raocnss or VULCANIZING RUBBER ANnrmwwmsnmybnmm 5 Application filed Eebruary 24, 1928. Serial No, 256,801. I

.NT FF asevidenced by the, characteristic eziainples hereinafter described, indicates that when a mercaptan compound isso treatedas to decrease its natural acidity, or conversely, to increase its basicity, the accelerating action offlthemodified mercaptan is considerably improved. r l

Various types of organic materials maybe employed to decreasethe acidic nature of mercapto compounds. Thus, for example,

one important class of bases which maybe employed to react with the mercaptansto produce compounds'havingvulcanizationaccel;

eratiiigproperties, is biguanide having the formula" 1 1 i i Naommnnu and its derivatives, articnlarly the aryl d rivatives. For example,triphenylbiguanide "hour, and a resinous material isflobtained upon allowing the mixtureto cool. This product, after gr nd ng, sincorporated in V the proportion of0.5 parts of accelerator-into amix comprising parts ofrubbergb parts ofzinc oxide and 3.5;partsof'fsulfur andfthe rubber compoundyulcanizedin a press in the f usualmanner forfabout an:hour1 atthe'temperature given by 20" pounds of steam" per 7 square inch. The resulting, product was M found to possessa tensile strengthatbreak of about 3000 "pounds per square inch." This sameacce'lerator may-likewisebe usedifor'the manufacture of a tread stock comprising 51 parts of rubber (smoked sheets), 20 parts of zinc oxide, 19 parts of carbon black, 3.5 parts of mineral rubber, 1.5 parts of sulfur, and 025 parts of accelerator. The product, after vulcanizing in a press, under the temperature given by 4.0 pounds steam pressure per square inch, for about an hour, was found to possess a tensile strength of approximately 3215 pounds per square inch, and an ultimate elongation of about 568%. Products possessing agreater tensile strength may readily be prepared by using a larger amount of accelerator, and preferably with aproportionate decrease in sulfur.

As another example of my preferred type of accelerators, ortho-tolyl-biguanide having the formula osn s/ may be heated together, preferably in equimolecular proportions at a temperature of 100 C. to 105 C. at which temperature they fuse and form a product solidifying to a resin on cooling. This resin is hard and can be ground when cold. Grinding is not necessary for compounding purposes, however, as the product fluxes readily. into the rubber. The reaction product obtained as described may be compounded in the well known manner in the proportion of 0.5 parts of accelerator, 100 parts of rubber (for example pale crepe rubber) 5 parts of zinc oxide, and 3 parts of sulfur, and the mixture vulcanized in a press at the temperature given by steam under 20 and pounds pressure per square inch. The following table shows the results of the tensile tests obtained by testing sheets of rubber vulcanized in a press for different periods of time at the temperatures obtained from and 10 pounds of steam pressure per square inch.

As another example of my preferred type of accelerators monophcnyl-biguanide having the formula and mercapto-benzo-thiazole having the formula may be heated together, preferably in equimolecular proportions, at a temperature of approximately 160 C. for about one hour at which temperature they fuse and form a produst which resinifies 011 cooling. The reaction product obtained as described may be compounded in the well known manner in the proportion of 0.5 parts of accelerator, 100 parts of rubber, for example smoked sheets, 5 parts of zinc oxide and 2.7 5 parts of sulfur, and the mixture vulcanized in a press at the tempera ture given by steam under 40 pounds pressure per square inch. The following table shows the results of the tensile tests obtained by testing sheets of rubber vulcanized in a press for different periods of time at the temperature obtained from 40 pounds of steam pressure per squire inch.

. Mpdilbluj o; elasiticity P e in s. in. at e onga- 1 of bul e stir: tions Tentsfle gtl n minpounds utes steam break Parts Smoked sheet rubber 51 Zinc oxide 20 Carbonblack; 19 Mineral rubber 3.5 Sulfur 1.5 Accelerator 0.25

The results of the tensile tests obtained by testing sheets of the above rubber vulcanized in a press for different periods of time at the temperature obtained from 40 pounds of steam pressure per square inch are given in 2 mercapto -benz1midazol; mercaptoqmina- A good hard'rubber product was obtained by vulcanizing the above stockfoi- 1 hour, minutes at pounds of steam pressure per square inch. The guanyl-ureas, iso-ureas,

thio-ureas and iso-thio-ureas are examples of other organic basic substances that may be reacted with non-volatile mercaptans to form compounds that are stable in the dry state.

Guanyl-urea having the formula for example reacts with mercapto-benzodi-ethyl-guanyl-thioureas may also be reacted with themercapto compounds to produceaccelerators of the type hereinbefore described.

7 Furthermore, it is to be understood that while I have specifically mentioned mercaptobenzo-thiazole as an example of a mercaptan, other compounds may, as I have found,rbe used successfully for the preparation of my preferred type of accelerators. Thus,I may use, as amercap'tah compound, aromatic mercaptans, such as thiophenol, thiocresol and the like; benzothiazole mercaptans and substitution products thereof, such as mercapto-tolylthiazole; the naphthyl-thiazole-inercaptans; thiooxy-indole osn 7 OH: H7

and substitution products thereof; amidothiophenols and derivatives; 2-mercaptothiazolin V V OHr-S j osn fi -j and derivatives; thethio-anilides the following table: I zole i CH c s11 Modulus of Time Pres 1 8 z E1011 gHwNH s.1n.a v of w sure elongationsof- 21 gatlon the thioamldes, and such compounds as thiommpounds I break at V utes steam break ammelin 30 40 1050 2490 2965 573 v, I f 45 40 1198 2685 3170 560 Allard rubbergwas Prepared as ithat is mercapto compounds preferably of Smoked sheetsnimm 100.0 the aromatic Series a Zinc oxide 15.0 The invention is to "be understood as not Sulfur 35,0 limited to the exact procedure followed or Reaction. product of' mercapto-benzo- P P P SB P Y dH} the foregolng examthia le d ph libi id 2 ples, which are illustrative only and not 11mitative of my invention. y'Moreover, the invention is to be considered as notlimited by any theories advanced in explanation of the chemical changes involved in the manufacture of the compounds set: forth but is limited solely a by the claims attached hereto as a part of a sible in viewofthe prior art;

What is claimed is: i 1. The processof vulcanizing rubber which comprises heating a mixture of rubber and sulfur in the presence of a vulcanization accelerator compr sing the reaction product of mercapto-benzo-thiazole and mono-phenylbi guanide. i i

2. The vulcanized rubber product produced by heating rubber and sulfurin the presence loc of a vulcanization accelerator comprising the a reaction product of mercapto-benzo-thiazole and mono-'phenyl-biguanide.

3. The process of vulcanizing rubber which comprisesheating rubber and sulfur in the presence of a vulcanization accelerator -comprising the reaction product of substantially equal-molecular proportions of mercaptobenzo-thiazole and mono-phenyl-biguanide. 4. The vulcanized rubber product produced by heating rubber and sulfur in the presence of a vulcanization accelerator com prising the reaction product of substantially equal molecular proportions of mercaptobenzo-thiazole and mono-phenyl-biguanide.

In testimony whereof I hereunto aflixmy signature. y a p a WINFIELD SCOTT. 

